Excessive secretions in airways alter airway flow characteristics, mucus clearance and aerosol deposition patterns. It also has been speculated that these alterations may be accentuated by two-phase interactions between gas and mucus layer. However, current knowledge of the gas-liquid two-phase interaction in airqays is scanty. The purpose of this study is to investigate 1) critical conditions for two phase gas-liquid flow in a horizontal rectangular flow channel model; 2) mucus transport by nonmucociliary two-phase interaction with continuous, periodic, and impulsive flows in a rigid and a flexible wall tube models; 3) deposition of aerosol particles in liquid lined tubes under the influence of wave motions of the liquid by using both the rigid and flexible wall tube model. Each study is carried out in conjucntion with gas velocity, liquid layer thickness, viscosity as well as elasticity of liquid. Since we wish to emphasize quantitative analysis, in vitro flow models will be utilized for the best control of experimental paramenters. A rectangular flow channel of 50 cm long and 3.0 cm width with variable depth is made with clear plastic to allow a direct observation of liquid motions. The variable channel depth allows us to change the cross section area of the channels. The channel is hinged at one end so that the slop of the channel can be varied to keep the liquid level constant. The rigid tube model consists of two identical glass tubes connected in series with a small gap between them so that a liquid can be supplied into the tube through the circumferential gap. The flexible wall tube model is made with latex rubber tubes and an excised sheep trachea and periodic pressure waves are applied to the tube to simulate the dimensional change during breathing. Both viscosity and clasticity of the liquid are measured by a double capillary viscometer and aerosol particles are generated by a vibrating orifice monodisperse aerosol generator with oleic acid solutions containing fluoresin tracer. Results of this study may reveal the nature of airway dynamics under the influence of excessive secretions, a mechanism of mucus clearance by two-phase interfacial forces in conjunction with rheologic properties of mucus and breathing patterns and the extent of overdose or over-exposure of patients with obstructive airway disease with inhaled medications, toxicants, or air pollutants.